Lymphocytic hypophysitis is a clinically rare disease, and it has been known to be an autoimmune disease which mainly affects pregnant women at the end of gestation or right after delivery. The authors experienced a case of lymphocytic hypophysitis in a 29-year-old pregnant woman with rapid progressing visual disturbance. Sella MRI showed a mass-like lesion of hypophysis and hypertrophy of pituitary stalk with evidences of hypopituitarism. Cesarean section was done and then TSA was performed. The pathologic diagnosis was lymphocytic hypophysitis. After TSA, visual acuity was improved and visual field defect was recovered. She was given thyroid hormone replacement therapy because of transient partial hypopituitarism for 6 months after surgery. One must consider the probability of lymphocytic hypophysitis, if there are alteration of visual acuity and visual field defect which aggravate rapidly during pregnancy due to mass effect, decreased serum hormonal levels shown in hypopituitarism and sella MRI findings of hypertrophy of pituitary stalk and enlargement of pituitary gland.